1. Field of the Invention
The present invention relates to a capacitor with excellent high-frequency characteristics, in which a couple of electrodes having a dielectric between them are made of a metal material, and more particularly relates to a structure of a capacitor suitable for mounting in an integrated circuit and a process for manufacturing this capacitor.
2. Description of Related Arts
As one of prior arts for speeding up the operation of an integrated circuit, which uses a unipolar transistor, such as a MOS transistor, or a bipolar transistor, the so-called copper wiring technology is well known which uses copper with lower electric resistance than aluminum to build circuit wiring previously formed by aluminum.
Regarding the capacitor used in an integrated circuit, it is known that a MIM (Metal-Insulator-Metal) capacitor is superior in high-frequency characteristics and more advantageous for improving the high-speed operation properties of the circuit than the so-called PIP (Polysilicon-Insulator-Polysilicon) capacitor in which a couple of electrodes having a dielectric between them are made of a conductive polysilicon.
It is also well known that it becomes possible to further improve the high-frequency characteristics of the integrated circuit by combining the above-mentioned copper wiring technology and technology for forming the electrodes of the MIM capacitor not by aluminum but by a copper metal material with lower electric resistance than aluminum.
However, the use of copper for the electrodes of the MIM capacitor as mentioned above gives rise to a phenomenon that part of the copper atoms constituting the electrodes diffuse into the dielectric made of silicon oxide, for example, between the electrodes of the capacitor. The diffusion of copper atoms into the dielectric deteriorates the insulation characteristics of the dielectric, and therefore decreases the dielectric property and the durability of the capacitor.
Furthermore, in shaping of the copper electrodes, it has been impossible to apply etching technology, which is used on the aluminum electrode, and therefore it has been difficult to form the copper electrodes in desired shape.
To solve the above problems, the present invention adopts the following configurations.
According to a first aspect of a capacitor of the present invention, the capacitor having a couple of electrodes with a dielectric placed therebetween, at least one of the couple of electrodes being made of copper, wherein the one electrode and the dielectric, a barrier is provided to prevent diffusion of copper into the dielectric.
The dielectric may be made of silicon oxide and the barrier may preferably be made of a conductive nitrided metal material, such as TaN or TiN.
The barrier effectively prevents the diffusion of copper atoms from the copper electrode into the dielectric, and therefore prevents the pollution of the dielectric by the copper electrode and effectively prevents a decrease in the insulating properties of the dielectric by the pollution mentioned above.
The conductive barrier securely prevents the pollution by copper without incurring a substantial increase in thickness of the dielectric of the capacitor, and hence without giving rise to unnecessary and harmful changes in capacity of the capacitor.
According to a second aspect of the present invention, a process for manufacturing a capacitor, wherein the capacitor has a couple of electrodes with a dielectric placed therebetween and at least one of the electrodes is made of copper and the capacitor is formed on a semiconductor substrate, comprises forming a nitrided metal film of a shape corresponding to a desired shape of the one electrode on the semiconductor substrate or the dielectric, and forming the one electrode on the nitrided metal film by electroplating using the nitrided metal film as the seed.
When the one electrode is used as the lower electrode, the nitrided metal film may be formed on the semiconductor substrate, the one electrode as the lower electrode may be formed on the nitrided metal film, a nitrided metal film to function as the barrier is formed on the lower electrode, the dielectric may be formed on the nitrided metal film, and the other electrode as the upper electrode may be formed on the dielectric.
When one electrode is used as the upper electrode, the nitrided metal film may be formed on the dielectric formed on the lower electrode, and the one electrode may be formed on the nitrided metal film on the dielectric.
Whether the one electrode is used for the lower electrode or the upper electrode, this electrode is formed by electroplating using the underlying nitrided metal film as the seed. Therefore, after the nitrided metal layer is formed and etched so as to have a desired pattern by photolithography and etching, the one electrode mentioned above may be formed by electroplating using the nitrided metal film as the seed. In this manner, the one electrode of a desired pattern may be formed relatively easily.
When the one electrode is used as the upper electrode, the nitrided metal film intervening between the upper electrode and the dielectric functions as the barrier to the diffusion of copper. Consequently, the nitrided metal film effectively prevents the diffusion of copper atoms from the upper electrode into the dielectric.